SEQUENCE STRATIGRAPHY IN THE UPPER CRETACEOUS OF THE BASCO-CANTABRIANBASIN (NORTHERN SPAIN)

The sedimentary cycles of the Cenomanian to Maastrichtian were investi gated in the Basco-Cantabrian Basin (BCB) in northern Spain (Provinces of Alava, Vizcaya and Burgos). The depositional area was a distally s teepened carbonate ramp which extended from Catalonia north-westwards to the Basque country. The investigated sediments range from calciturb idites and pelagic marls to marl - limestone alternations deposited on a distal carbonate ramp. Shallow marine limestones, marls and interti dal clastics and carbonates were deposited on the proximal part of the carbonate ramp. The establishment of a regional sequence analysis is based on the investigation of seismic profiles, well logs and outcrop sections. Examples of outcrop sections are interpreted in terms of seq uence stratigraphy (unconformities of third- and second-order cycles, depositional geometries, systems tracts). The sequence stratigraphic i nterpretation of outcrop sections is based on facies analysis, interpr etation of observed depositional geometries and correlation of unconfo rmities and marine flooding surfaces through the basin. A biostratigra phic framework is established based on ammonites, inoceramids, plankto nic and benthic foraminifera. As a result, a regional sequence stratig raphic cycle chart is presented and compared with published global cyc le charts. The correlation of the regional cycle chart with published cycle charts is good. In the Cenomanian and Turonian, several sequence boundaries in the BCB are shifted by up to one biozone compared with the global chart. Some type 1 boundaries of the standard chart are onl y type 2 in the BCB. Important type 1 boundaries in the BCB are: top G eslinianum Zone with a 100 m lowstand wedge at the basis of the sequen ce (sequence boundary 92.2); base Petrocoriense Zone with a 250 m shal lowing-upwards lowstand wedge at the basis (sequence boundary 89.2); a nd within the Syrtale Zone (sequence boundary 85.0). The Campanian - M aastrichtian sequence record is strongly disturbed by local compressiv e tectonics. Several sequences are recognizable and can be correlated with the global cycle chart. Correlation is hampered by the low biostr atigraphic resolution in the western basin part. Subsidence analysis o f several sections of the Upper Cretaceous of the BCB and its interpre tation in the regional tectonic context leads to a discussion of the c auses of the observed cyclicity. A regional eustatic curve is presente d for the Upper Cretaceous of the BCB. Stage and substage names were u sed according Code-Committee (1977).